I distinguish two senses in which one can take a given physical theory to be `complete'. On the first, a complete physical theory is one that, in principle, completely describes physical reality. On the second, a complete physical theory is one that provides all of the conceptual resources one needs to describe any (in general probabilistic) physical phenomenon to any level of detail one likes, in principle. I argue that while the (neo-)Everettian approach to interpreting quantum mechanics aims to show that it is complete in the first sense, the (neo-)Bohrian approach begins from an understanding of quantum mechanics as being complete in the second sense. I then discuss some of the essential differences between how classical and quantum theory describe phenomena, and the way in which the quantum description can be thought of as a ``natural generalisation'' (to use Bohr's phrase) of the classical description. Finally, I elaborate upon the two visions of physics from which one can motivate the first and the second sense of completeness, respectively: \emph{metaphysical realism}, on the one hand, and what I will call \emph{methodological realism}, on the other -- and discuss what one can say about the significance of the differences between quantum and classical description from each of these points of view. I suggest that there is a sense in which the views of (neo-)Everett and the views of (neo-)Bohr can be understood to be mutually supporting positions, from their respective perspectives, even though they are diametrically opposed.
I distinguish two senses in which one can take a given physical theory to be `complete'. On the first, a complete physical theory is one that, in principle, completely describes physical reality. On the second, a complete physical theory is one that provides all of the conceptual resources one needs to describe any (in general probabilistic) physical phenomenon to any level of detail one likes, in principle. I argue that while the (neo-)Everettian approach to interpreting quantum mechanics aims to show that it is complete in the first sense, the (neo-)Bohrian approach begins from an understanding of quantum mechanics as being complete in the second sense. I then discuss some of the essential differences between how classical and quantum theory describe phenomena, and the way in which the quantum description can be thought of as a ``natural generalisation'' (to use Bohr's phrase) of the classical description. Finally, I elaborate upon the two visions of physics from which one can motivate the first and the second sense of completeness, respectively: \emph{metaphysical realism}, on the one hand, and what I will call \emph{methodological realism}, on the other -- and discuss what one can say about the significance of the differences between quantum and classical description from each of these points of view. I suggest that there is a sense in which the views of (neo-)Everett and the views of (neo-)Bohr can be understood to be mutually supporting positions, from their respective perspectives, even though they are diametrically opposed.
This work presents a historical-epistemological analysis of the foundations of quantum mechanics. From a philosophical point of view, the relationships between quantum mechanics and scientific realism are highlighted, as well as the influence of the neo-positivist philosophy of the first decades of the 20th century. The great significance of measurement in the context of quantum mechanics is underlined, as an essential element in providing a coherent description of reality moving from the microcosm to the macrocosm, as well as the role that the measurement apparatus and the consciousness of the observer assume during the act of measurement, the ontological problem, the problem of the objectification of the wave function and the problem of the definition of discernibility. This is followed by an overview of the most important alternative proposals to the standard interpretation (Copenhagen interpretation), with particular reference to hidden variable theories, and other alternatives to standard quantum mechanics that profoundly modify the vision of reality, such as the Everett’s many-worlds theory, the QBism, the unified holistic approach.
When we are presented with apparently bizarre properties of microsystems governed by quantum mechanics (as in our discussion of the double-slit experiment in the previous chapter), we naturally ask whether it might be possible to find another theory, or at least another story to go with the equations, that would make more sense to us. We might seek a theory and a view of fundamental physical processes that would accord more with our classically based, everyday common sense. This typically takes the form of the question of the possibility of the existence of a more detailed description of atomic processes than that afforded by the wave function (that is, by the Copenhagen interpretation of the previous chapter). In this chapter we discuss some of the central interpretive problems of the Copenhagen version of quantum mechanics. Then, in the next two chapters, we look at the severe, general restrictions that are placed on any such completion of quantum mechanics and at one particular extension of quantum mechanics. First, though, we begin here with the struggle that ensued over the status of causality in quantum theory. THE COMPLETENESS OF QUANTUM MECHANICS Although the Heisenberg uncertainty principle (Section 20.4) and the lack of absolute predictive power are an inherent feature of quantum mechanics, there have been attempts to preserve an in principle completely deterministic structure for physics. Even classically, in a macroscopic sample of gas there are so many molecules that it would be hopeless, as a practical matter, to predict the future locations of all these molecules from Newton's laws of motion.
I reinterpret Bohr's attitude towards quantum mechanical formalism and its empirical content, based on his understanding of the correspondence principle and its approximate applicability. I suggest that Bohr understood complementarity as a limitation imposed by the commutation relations upon the applicability of the idealizations which had grounded the use of the correspondence principle. By discussing this interpretation against the contemporary background of discussions regarding “naïve realism” about operators (as observables), I suggest that a Bohrian view on the empirical content of quantum mechanical operators may provide a middle ground between complete contextualism and an untenable realism about quantum properties.
We begin by discussing ``What exists?'', i.e. ontology, in Classical Physics which provided a description of physical phenomena at the macroscopic level. The microworld however necessitates a introduction of Quantum ideas for its understanding. It is almost certain that the world is quantum mechanical at both microscopic as well as at macroscopic level. The problem of ontology of a Quantum world is a difficult one. It also depends on which interpretation is used. We first discuss some interpretations in which Quantum Mechanics does not provide a complete framework but has to be supplemented by extra ingredients e.g. (i) Copenhagen group of interpretations associated with the names of Niels Bohr, Heisenberg, von-Neumann, and (ii) de-Broglie-Bohm interpretations. We then look at some interpretations in which Quantum mechanics is supposed to provide the entire framework such as (i) Everett-deWitt many world, (ii) quantum histories interpretations. We conclude with some remarks on the rigidity of the formalism of quantum mechanics, which is sharp contrast to it's ontological fluidity.
The so-called “orthodox” interpretation of quantum physics attributed to Niels Bohr is commonly regarded as abandoning realism. I have already opposed this view elsewhere (Folse 1985) but partially in response to criticism of my position (Shimony 1985), here I propose to relate Bohr’s realism to recent contributions to the realism debate given by Hacking (1983), Cartwright (1983), and Ellis (1985). Specifically, I argue that Bohr’s complementarity viewpoint requires a causal entity realism. Furthermore, labeling Bohr an anti-realist with respect to theories is misleading because it assumes the correspondence theory of truth that Bohr holds quantum theory forces us to reject. Although there are many realist views, I take the root of realism to be the quest for knowledge about the reality producing the phenomena we experience. It is realism in this sense that Bohr defended and that makes science significant to metaphysics.
Abstract There is a deeply entrenched view in philosophy and physics, the closed systems view, according to which isolated systems are conceived of as fundamental. On this view, when a system is evolving under the influence of its environment, this is always described in terms of a coupling between it and a separate system which taken together are isolated. In this chapter, we introduce the theoretical framework that we call standard quantum theory (ST), formulated in accordance with the closed systems view, and we consider approaches to interpreting the formalism of ST that take it to be complete in some sense. Broadly speaking, these can be grouped into two families. The first includes (neo-)Bohrian and related approaches, the second (neo-)Everettian. We argue, from the point of view of each, that although ST is formulated in accordance with the closed systems view, it is nevertheless ontologically committed to open systems in a way that other, for instance, classical, theoretical frameworks are not. We close with the suggestion that philosophical and foundational progress may be made through the adoption of an alternative theoretical framework, which might in principle involve a change in corresponding view, within which one can make sense of open systems dynamics in fundamental terms.